Here are three ways to buy tickets (and, in the first two
cases, Tourist Travel Cards):

From
an ACTV or Hellovenezia ticket office.
You'll find a biglietteria or "ticket point"
at most larger vaporetto stations, such as Piazzale Roma, Ferrovia (along the
water by the railroad station), Rialto, San Marco Vallaresso, and Zaccaria (on
the waterfront above the Piazza San Marco and the Doge's Palace).
Business hours vary, but if the ticket point is closed, you
can use a machine.

From
a ticket-vending machine. Touch-screen machines are now available in many ACTV
locations, either to replace manned booths or to provide backup at busy times or
after hours. For illustrated step-by-step instructions on how to use the
machines, see our ACTV Ticket Machines
article.

From
the boat attendant.If you board a vaporetto or motoscafo at a
stop that doesn't have a ticket point or machine, ask the attendant for a ticket
(biglietto) as soon as you're on board. Don't dawdle: If you're caught
without a ticket, you'll be liable for a hefty fine.

Tip:The old cardboard ACTV tickets have mostly been replaced by
rechargeable tickets such as the biglietto ricaricabile shown here. If
you pay for two or three tickets at a newsstand or ACTV ticket counter and
you're handed only one biglietto, don't worry--several fares are stored
on the ticket, and you can present it for recharging when you want to buy more
fares.